1. Field of the Invention
The present invention generally relates to tank venting valves for relieving the internal pressure or vacuum in tanks at a predetermined pressure/vacuum. More particularly this invention relates to weight/spring loaded tank vents. More particularly the invention relates to tank venting valves for use in sanitary service for processing food and pharmaceuticals.
2. Related Art
The basic valve design is known as a “weight loaded tank vent”. The design utilizes a weighted cover over a nozzle. The cover, also known as a pallet, forms a barrier to the nozzle opening. The weight of the pallet determines at what pressure the pallet will lift open to relieve pressure in the tank. The opening pressure is known as the “set pressure”. The set pressure can easily be determined by dividing the weight of the pallet assembly by the open area of the nozzle. If a higher set pressure is desired, more weight is added to the pallet.
Another type of pressure relieving device is a spring loaded tank vent. The spring loaded type is used for set pressures above that which is practical for weight loaded operation due to either a high set pressure and there is not enough room for the weights on the pallet or where the size of the vent nozzle dictates a large weight on the pallet.
A third type of tank vent is pilot operated. Pilot operated tank vents utilize the tank pressure acting on an area larger than the nozzle area to create a higher downward force to hold down a pallet or seat plate against the tank pressure. For this reason pilot operated tank vents seal tighter than weight or spring loaded vents until the set or opening pressure is reached. The set pressure is adjustable by means of a spring in the pilot.